Printing apparatuses such as photocopiers and printers typically have a fixing device for fixing a transferred toner image to a printer sheet.
Such a fixing device performs the image fixation by thermo-compressing a printer sheet on which an image is transferred, using a fixing roller (a pair of rollers).
In the fixing device, a releasing agent such as silicone oil is supplied (applied) to the surface of the fixing roller. This is performed to prevent the image from being transferred to the fixing roller (i.e. offset of the image) and to prevent the printer sheet from being entangled with the fixing roller, in order to stably perform the image fixation.
The aforesaid application of oil is described in the patent documents 1 through 3. (patent document 1: Japanese Laid-Open Patent Application No. 8-137317/1996 (Tokukaihei 8-137317; published on May 31, 1996); patent document 2: Japanese Laid-Open Patent Application No. 2002-278345 (Tokukai 2002-278345; published on Sep. 27, 2002); patent document 3: Japanese Laid-Open Patent Application No. 2003-122167 (Tokukai 2003-122167; published on Apr. 25, 2003))
FIGS. 24 and 25 illustrate a conventional art of applying oil to a fixing roller, described in the patent documents 2 and 3.
As shown in these figures, according to the conventional art, oil is sucked up from an oil tank 104 that always store the oil to a pipe-shaped member 105 and to which oil can be injected from the outside, by a piezo pump (or electromagnetic pump) 103 located above the oil tank 104, and consequently the oil is supplied to a pipe-shaped member 101.
On the upper side of this pipe-shaped member 101, a plurality of holes (oil excretory holes) are made along the longitudinal direction. On the lower side of the pipe-shaped member 101, there are (i) a felt 106 for collecting the oil showering down thereon from the pipe-shaped member 101 and (ii) an application roller 107 for applying the oil in the felt (releasing agent supplying felt) 106 to the fixing roller (application target member) 102.
The lowest stream (tip) of the pipe-shaped member 101 has been subjected to a process of preventing the oil leakage (e.g. a caulking process by which the tip is caulked by stamping and the like). With this, the oil does not leak except from the aforesaid holes.
The redundant oil not applied to the fixing roller 102 and still remaining in the felt 106 is collected by a concave oil pan (releasing agent collecting pan) 108 provided below the felt 106. The oil then returns to the oil tank 104 though a tube-shaped member 109 connected to the oil pan 108.
In the oil tank 104, a sensor 110 for detecting the remaining amount of the oil is provided. This sensor 110 detects the amount of the oil remaining in the tank, and transmits the result of the detection to a control section of the printing apparatus.
With this, when the remaining amount of the oil is small, a display panel and the like on the main body of the printing apparatus prompts the user to supply oil, or the printing by the printing apparatus is temporarily brought to a halt.
When the oil supply is insufficient at some parts of the fixing roller 102 in the longitudinal direction, the aforesaid offset of the image and the entanglement of the printer sheet occur. To prevent them, it is very important to evenly supply the oil (i.e. balance an amount of the supplied oil) along the longitudinal direction of the fixing roller 102.
For this reason, according the conventional art, all holes of the pipe-shaped member 101 face upward (i.e. made on the upper side of the pipe-shaped member 101). This allows the oil to be simultaneously discharged from all holes, when the printing apparatus is horizontally provided (i.e. in a normal state).
In the aforesaid conventional art, only the felt and the application roller are provided as intermediate members that are provided between the pipe and the fixing roller and spread the oil in the longitudinal direction.
For this reason, the oil may not be sufficiently spread and the oil application may not be evenly done in the longitudinal direction, when the oil has a relatively high viscosity.
To solve this problem, the patent documents 2 and 3teach that a guide member is attached to the pipe-shaped member 101, thereby achieving the evenness.
However, according to these conventional arts teaching that the guide member is provided for spreading the oil, the guide member is provided in the vicinity of the application roller touching the fixing roller. On this account, the oil flowing on the guiding member may be deteriorated by the heat from the application roller.
Also, according to these conventional arts teaching that the guide member is provided for spreading the oil, the spreading of the oil is performed solely by the capillary phenomenon of the felt. On this account, there is still a possibility that the oil is not sufficiently spread and not evenly applied in the longitudinal direction.
Furthermore, in the conventional arts where the oil discharged from the pipe permeates a guide part (felt) so that the spreading of the oil is performed, the guide part is closely in touch with the pipe. For this reason, the oil spreading along the longitudinal direction of the pipe solely depends on the capillary phenomenon of the guide section, so that the oil spreading cannot be evenly performed.